Hydraulic snubbing device for presses



Jan. 6, 1970' y, B As, JR" ET AL 3,488,045

HYDRAULIC SNUBBING DEVICE FOR PRESSES Filed Jan. 26, 1968 NW3 m H a &

US. Cl. 267-1 11 Claims ABSTRACT OF THE DISCLOSURE A pneumatic die cushion of the type utilized in presses and including a movable member and a stationary membet. The improvement comprises hydraulic snubbing means for cushioning the movement of the die cushion as it approaches the limit of its movement in one direction by forcing a fluid from a groove in one of the members into a chamber in the other member through an increasingly restrictive orifice.

The present invention pertains to the art of pneumatic die cushions and, more particularly, to an improved die cushion having hydraulic snubbing means for dissipating energy during a portion of the operating cycle thereof.

The present invention is particularly applicable for use in metal working presses for dissipating the energy of the return movement of the die cushion assembly and it will be discussed with particular reference thereto; however, it is to be appreciated that the invention has much broader applications and may be used in various similar machine operations which require energy dissipation of a moving part.

In the design, manufacture and use of punch presses and the like, it is common to provide a cushion assembly to absorb the impact of the movable ram engaging the stationary die structure on which is mounted the workpiece. Such cushion assembly may take the form of a cushion pressure pad mounted on a movable member and .which moves relative to a stationary member as a piston and cylinder. Pneumatic pressure is provided beneath the cushion pressure pad to absorb the impact of the blow of the ram against the stationary die structure. After absorbing such impact, it is necessary for the cushion pad to return to its static position for the next cycling of the machine, and, the considerable amount of energy generated by the air pressure and the inertial eifects in stopping must be absorbed or dissipated in a suitable manner. The present method of stopping the return movement of the cushion assembly is to run the pressure pad against a fixed stop at the top of the pad stroke, as by impacting on a flange that is supported on the frame of the machine. Thus, energy is dissipated by metal distortion and the continually repeated shock loading causes detrimental eifects, not only to the flange and the machine frame, but also to the cushion structure in general. Repair and replacement of parts which are damaged as a result is an extremely expensive undertaking, both in terms of damaged parts and in terms of the time during which the machine is inoperative. Accordingly, there has been a demand for a method of dissipating the energy of the return stroke of the cushion assembly in such a way as to dissipate such energy without metal-to-metal contact and thereby increase the life and efiiciency of the cushion assembly and the machine.

The present invention is directed toward an hydraulic snubbing device that will dissipate the energy of the return stroke of the movable member in the die cushion assembly by means of an incompressible fluid being moved United States Patent from one location to another, and in such way as to absorb the shock and inertia of the movab e portion of the die cushion assembly to reduce the repair and main tenance expense and to increase the efiiciency of a large machine.

In accordance with the present invention, there is provided an hydraulic snubbing device comprising means for dissipating the energy of the stroke of the cushion pad assembly by forcing fluid from one location to another at a varying rate.

In accordance with another aspect of the present invention, there is provided apparatus for dissipating the energy of the return stroke of the cushion pad assembly by forcing fluid from one location to another through an increasingly restricted orifice.

In accordance with still a further aspect of the present invention, there is provided means in the movable portion of the cushion pad assembly to retain a fluid during the down stroke thereof, and a chamber in the stationary portion of the assembly to receive fluid from such means at a varying rate.

In accordance with yet a further aspect of the present invention, there is provided a fluid retaining groove in the movable member of the cushion pad assembly and a flange on the stationary member of the assembly, such flange being receivable in the groove and having a frustoconical surface thereon, the surface forming, with an edge of the groove, an annular increasingly restricted orifice as said movable member approaches the limits of its return stroke.

The primary object of the present invention is the provision of a die cushion having a hydraulic snubbing device to dissipate the energy of the return stroke of the die cushion assembly.

Another object of the present invention is the provision of apparatus of the type described which is especially suited for use in metal working presses.

Yet another object of the present invention is the provision of means on the movable and stationary members of a die cushion assembly to transfer a fluid from one location to another at a varying rate to dissipate the energy movement of the movable member as it approached the limit of its return stroke movement.

These and other objects and advantages will become apparent from the following description used to illustrate a preferred embodiment of the present invention as read in connection with the accompanying drawings in which:

FIGURE 1 is a cross-sectional view of a press machine illustrating the position of the parts thereof in one condition of operation and showing a die cushion assembly constructed in accordance with the present invention;

FIGURE 2 is an enlarged cross-sectional view of the structure illustrated in FIGURE 1, showing the preferred embodiment of the present invention in one position of operation; and

FIGURE 3 is an enlarged cross-sectional view of a portion of the structure illustrated in FIGURE 1 showing that preferred embodiment of the present invention in another position of operation.

Referring more particularly to the drawing, wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, FIGURE 1 shows a portion of a machine press of the type used to carry out cutting, bending, forming or other operations on a workpiece, indicated by the numeral 10, mounted on the machine. The machine includes a base or frame structure, a portion of which is indicated at 12 and in which is mounted, in a manner well known in the art, a vertically movable ram assembly, indicated generally by the numeral 14. Mounted in the ram 14 is a relatively movable die or punch 16, the punch having a shaft or stem 18 connected to a suitable operating mechanism for movement relative to the ram assembly 14.

Disposed on the frame 12 is a stationary die structure, indicated generally by the numeral 20, on which is received the workpiece for the purposes to become hereinafter more particularly described. Stationary die 20 is secured to a mounting plate 22 in any suitable manner, as by bolts 24, the plate 22 being secured to the bolster or bedplate 26 which in turn is secured to, or supported from, the machine frame 12 by uprights or the like 28.

Disposed within the stationary die structure 20 is a die plate or pad, indicated generally by the numeral 30, which includes a plate member 32 and a plurality of die pins 34 extending downwardly therefrom through suitable apertures in the plate member 22 and the bolster 26. Pad 32 underlies the workpiece 10 and is intended to back up the workpiece 10 as the forming operation is being carried out by means of the movable die or punch 16 in the ram structure 14.

Disposed below the bolster or bedplate 26 is the die cushion assembly, illustrated generally by the numeral 36. Such assembly includes a stationary member, indicated generally by the numeral 38, having an outwardly directed flange 40 at the base thereof for securement to the frame 12 by bolts or the like 42. Surrounding the stationary member 38 is a movable member, indicated generally by the numeral 44, which closely surrounds the stationary member 38 for purposes to become hereinafter more apparent. Movable member 44 is secured to a cushion pressure pad 46 by an outwardly directed flange 48 and a plurality of bolts or the like 50. Pressure pad 46 receives the lower end of the die pins 34, the pins being received in suitable recesses 52 formed in the pressure pad 46 to maintain the pins 34' and the die plate 32 in proper alignment.

Stationary member 38 and movable member 44 are pro vided with hollow interiors 54 and 56 respectively, to form an air pressure chamber receiving compressed air from any suitable source, for absorbing the impact of the ram structure 14 and die or punch 16 as they descend upon the stationary die 20 and the workpiece 10. In the normal operation of the machine, the movable portion of the die cushion assembly 36, through the downward movement of the die plate and the cushion pressure pad 46, moves downwardly about the stationary member 38 against the pressure of the compressed air in the chambers 54 and 56 to absorb the impact on the die plate 32. When the ram structure moves upwardly, thus disengaging from the die pad 32, the compressed air in the chambers 54 and 56 will cause the movable portion of the die cushion assembly 36, including the movable member 44 and the cushion pad 46, to return to a full upward position.

To dissipate the energy of the pressure pad 46, generated by the compressed air in the chamber 54 and 56 and the inertial effects in stopping, the hydraulic snubbing apparatus of the present invention is provided. Secured to the lower end of the movable member 44 is an annular seal retaining ring 58, secured to the movable member 44 in any suitable manner as by bolts 60. Retaining ring 58 extends radially inwardly to approach the outer surface of the stationary member 38 and is formed to provide an annular fluid retaining groove 62. At one position around the circumference of the ring 58 is a radial bore 64, terminating radially inwardly in the side wall of the retaining ring 58 and at the upper level of the groove 62 formed therein. Suitably attached in the retaining ring bore 64 is a conduit 66, through which the fluid in the groove 62 may be maintained at the proper level.

Adjacent the groove 62 in the retaining ring 58, and radially inward thereof, is a flexible seal 68 adapted to engage the outer surface of the stationary member 38, as will become hereinafter more particularly described. Seal 68 is maintained in a suitable recess 70 in the retaining ring 58 in any suitable manner, as by a retaining ring 72.

The upper portion of the stationary member 38 is provided with a downwardly depending annular flange 72 which is receivable in the annular groove 62 formed in the seal retaining member 58. Flange 74 defines, with the side wall of the stationary member 38, an accumulator groove or chamber 76 which is in communication with the fluid retaining groove 62 in the movable member 44. Seal 68, engaging a side wall of the groove or chamber 76, restricts communication between the chamber 76 and the groove 62.

The lower and inward end surface of the flange 74 is formed with a frusto-conical surface 78, which opposes an edge or corner of the annular groove 62 in the seal retaining member 58. Frusto-conical surface 78 and adjacent groove edge 80 provide an increasingly restricted annular orifice for passage of fluid from the groove 62 to the chamber 76 with upward movement of the movable member 44 and the retaining ring 58.

With reference now to FIGURES 2 and 3, the operation of the hydraulic snubbing means will be described. It will be assumed for purposes of illustration that the ram structure 14, die plate structure 30, cushion pressure pad 46 and movable member 44 have been moved downwardly, as a result of the ram impact, such that the retaining ring member 58 assumes the position illustrated in dashed and dotted lines 58 in FIGURE 2. In such position fluid 82 will fill the groove 62 in the retaining ring and the flange 74 will be displaced therefrom. As the movable portion 44 of the die cushion assembly 36 moved upwardly under the pressure of the air in the chambers 54 and 56, the flange 74 of the stationary member will first cut off communication through the drain and refill bore 64 to the groove 62. At such point the seal 68 contacts the inward surface of the annular chamber 76 in the stationary member 38, providing direct communications between the groove 62 and the annular chamber 76. As the movable portion 44 continues its upward movement, the frusto-conical surface 78 and the groove edge 80 decrease the size of the annular flow orifice between the groove 62 and the chamber 76, causing the fluid to flow at such a rate as to dissipate the energy of movement and stoppage of the movable portion 44 toward its upward position. When the movable member 44 is in the complete upward position, and when the flange 74 is fully received in the groove 62 as illustrated in FIGURE 3, the fluid will have been moved from the groove 62 to the chamber 76 and will have absorbed the energy of the movable structure. As the machine is again cycled and the movable structure forced downwardly, the fluid will flow freely from the accumulator chamber 76 to the groove 62 through the now increasing annular orifice between the frusto-conical surface 78 and the groove edge 80. As the seal 68 pulls away from the wall of chamber 76 the fluid will have completely flowed into the groove 62 and any lost fluid may be replaced through the drain and refill bore 64. The machine and snubbing device are now in position for further like cycles of operation.

In order to prevent loss of fluid through mating surfaces, such as between the seal ring 58 and the movable member 44 and between the stationary member 38 and the movable member 44, suitable seals and gaskets, such as O-ring 84 and annular wiper seal 86, may be provided.

Having thus described our invention, we claim:

1. Hydraulic snubbing means for a machine having a cushion assembly including a movable member and a stationary member, said snubbing means comprising annular groove means in one of said members, annular chamber means in the other of said members and in communication with said groove means in said one mem ber fluid in said groove means, means for causing said fluid to flow from said groove means to said chamber means for increasingly restricting flow of said fluid from said groove means to said chamber means as said movable member approaches the limit of movement thereof in one direction.

2. Hydraulic snubbing means for a machine having a stationary member and a reciprocating member movable relative thereto, said snubbing means comprising an annular groove in said reciprocating member, an annular flange on said stationary member receivable in said groove and having a surface adjacent said groove angularly inwardly formed to provide a varying orifice with one edge of said groove, a seal member mounted in said reciprocating member and engaging said stationary member radially inwardly of said flange and defining with said flange an annular accumulator chamber communicating with said groove, and a volume of fluid in said annular groove adapted to be forced through said varying orifice as said reciprocating member approaches said flange on said stationary member to dissipate the energy of said reciprocating member as said reciprocating member approaches the limit of movement thereof in one direction.

3. Hydraulic snubbing means for a machine having a cushion assembly including a stationary member and a member movable relative thereto, said snubbing means comprising an annular portion on said movable member surrounding said stationary member and having an annular fluid retaining groove formed therein, annular chamber means in said stationary member communicating with said groove, fluid in said annular groove, and means on said stationary member adjacent said chamber and receivable in said groove for increasingly restricting flow of said fluid from said groove to said chamber means as said movable member approaches the limit of movement thereof in one direction.

4. Hydraulic snubbing means for a machine having a cushion assembly including a movable member and a stationary member, said snubbing means comprising an annular portion of said annular member surrounding said stationary member and having an annular fluid retaining groove formed therein, an annular flange on said stationary member receivable in said groove in said movable member, said flange forming with said stationary member an annular chamber communicating with said groove, fluid in said groove, and means for forcing said fluid from said groove to said chamber at an increasingly restrictive rate as said movable member approaches the limit of movement thereof in one direction.

5. The hydraulic snubbing means set forth in claim 4 wherein said means for forcing said fluid from said groove to said chamber includes a frusto-conical surface on said flange, said surface and one edge of said groove forming an increasingly restrictive orifice for fluid flow from said groove to said chamber.

6. The hydraulic snubbing means set forth in claim 4 and further including an annular seal mounted in said movable member adjacent said groove and engageable with a wall of said chamber in said stationary member.

7. The hydraulic snubbing means set forth in claim 4 and further including conduit means extending through said movable member and communicating with said groove for conveying fluid thereto and therefrom to maintain the level of fluid therein.

8. Hydraulic snubbing means for a machine having a cushion assembly including a movable member and a stationary member, said snubbing means comprising an annular portion on said movable member surrounding said stationary member and having an annular fluid retaining groove formed therein, an annular flange on said stationary member and spaced radially outwardly therefrom and forming therewith an annular groove communicating with said annular groove in said movable member and being oppositely disposed relative thereto, said flange being receivable in said annular groove in said movable member as said movable member ap proaches the limit of movement thereof in one direction, a frusto-conical surface on the radially inward portion of said flange and adjacent one edge of said groove in said movable member and defining an increasingly restrictive annular orifice with said one edge of said groove as said movable member approaches said limit of movement thereof, an annular seal member secured in said annular portion of said movable member and radially inwardly and adjacent said annular groove therein, said seal being engageable with said stationary member to define With said flange an annular fluid receiving chamber, and a fluid in said annular groove in said movable member and adapted to be forced through said increasingly restricted orifice as said movable member approaches said limit of movement thereof to dissipate the stopping energy of said movable member.

9. In a die cushion assembly including a movable member and a stationary member, said members coacting to form a cushion chamber having a volume which varies as said movable member moves between two extreme positions, the improvement comprising: a cavity in one of said members, an element on the other of said members, said elements movable into said cavity when said movable member approaches one of said extreme positions, an outlet communicated with said cavity at least When said movable member approaches said one position, a fluid in said cavity and displaceable through said outlet, and said outlet forming a restriction to flow of said fluid from said cavity to cushion movement of said movable member toward said one position.

10. The improvement as defined in claim 9 wherein said outlet is defined by said element.

11. The improvement as defined in claim 10 wherein said element is contoured to provide an increasing restrlctive outlet.

References Cited UNITED STATES PATENTS 2,918,272 12/1959 Williamson 267-1 JAMES B. MARBERT, Primary Examiner 

